Rhythmic structures are a set of repeated rhythmic gestures that work with other melodic phrases within a given composition.
Consider the following semi rhythmic etude:
Rhythmic structure is created by kick and snare drums played with the right and left feet.
Melodic phrases are played on roto toms (right hand).
Hi-hat and or cymbals (left hand) can be added for additional accents or gestures that would aid melodic phrases.
Rhythmic Structure Example: